JPS5832734B2 - How to introduce gas into a sealed container - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The invention relates to a method for introducing a gas, for example tritium, into a closed container, such as a gas discharge tube, which is designed as an overvoltage protector.

In this regard, tritium acts in a well-known manner as an ionizing radioactive medium to stabilize the operating voltage of the overvoltage protector.

A conventionally known method for introducing tritium into a gas discharge tube is to include tritium as an additive in the filling gas, and then introduce the filling gas containing tritium as the additive into the gas discharge tube. be.

This conventional method can be applied without any problems when manufacturing discharge tubes, each of which is equipped with a pump pipe.

Specifically, in this conventional method, when filling gas, the pump pipe provided in each gas discharge tube is connected to a completely sealed gas refilling device, and the gas discharge tube is charged through the pump pipe. This allows gas to be introduced into each of the parts.

Therefore, although this method does not pose any problem of releasing radioactive gas, the pump pipes provided in each gas discharge tube are connected to a gas filling device one by one to introduce gas into the gas discharge tube. As a result, there is a problem of inferior production.

On the other hand, many gas discharge tubes without pump pipes as described above are put into a furnace at once in one sealed brazing tube, and the brazing tubes send gas into the furnace. There is also a method of introducing gas into a gas discharge tube and then sealing the gas discharge tube by brazing.

This method is excellent in productivity because it introduces gas into many discharge tubes at once, but after introducing gas into the discharge tube, the discharge tube filled with gas is sealed by brazing. Therefore, when brazing, a large amount of gas remains in the furnace, and the brazing becomes contaminated during the work, so unless a complicated purification process is applied to the gas, the gas must be reused. I can't do that,
It has no choice but to be released into the atmosphere using an evacuation device.

However, when introducing gas into the gas discharge tube using this method, the gas introduced into the gas discharge tube is 1
Since the tritium component is contained up to 0 μCi AttyAl 0000Ci/m 2 , it is extremely difficult to satisfy the total amount of tritium emission regulations and the tritium concentration regulations in the discharged air using this method.

An object of the present invention is to provide a method for introducing gas into a closed container that enables reuse of discharge gas.

An object of the present invention is to seal a hermetically sealed container such as a gas discharge tube formed as an overvoltage protector, and then diffuse gas through the wall of the hermetically sealed container to introduce gas into the sealed container. This is achieved by allowing the diffusion to occur at a temperature lower than the temperature at which the closed container is sealed.

As described above, in the method according to the present invention, after the sealed container is sealed, the gas is introduced into the sealed container by diffusing the gas through the wall of the sealed container. The remaining gas is not contaminated by the sealing operation of the sealed container, and the effect is that the gas can be recovered and reused as is.

The gas introduction method according to the invention is based on the principle that light gases such as eg helium hydrogen, tritium, etc. can diffuse through solid materials such as glass, ceramics, metals, etc.

The total amount of gas q that diffuses or permeates through a glass or ceramic wall is determined by the following diffusion equation, which is well known to those skilled in the art.

That is, where A is the area of the wall made of glass or ceramic, d is the thickness of the wall, K is the permeation rate constant, t is time, and PI I)2 is It is the pressure difference between the high pressure side and the low pressure side.

Further, K is a function dependent on temperature, and is given by the following equation.

That is, K-=Ce-Q/RT
(2) where C is a constant, Q is the activation energy of the wall material, R is the gas constant, and T is at temperature 0.

That is, the above equation (1) shows how much gas is diffused through the glass or ceramic wall over time, and if the temperature is constant, the above equation From equation (2), K is constant.

Therefore, by properly selecting the parameters of the gas introduction operation, i.e. pressure, temperature and time, it is possible to diffuse and introduce the desired amount of tritium into a closed vessel with walls at least partially made of glass or ceramic. is possible.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

The gas discharge tube shown in FIG. 1 in the form of a closed vessel, i.e. an overvoltage protector, consists of two electrodes 1 and 2, each provided with a flange, and a glass or ceramic material arranged between the flanges of these electrodes. These electrodes 1, 2 and the insulating wall 3 have a ring-shaped insulating wall 3 formed by hard brazing between the flange of the electrode and the sintered metal coated on the end face of the insulating wall. The joints 4 and 5 are airtightly joined.

The height of the insulating wall 3 is determined so that a predetermined discharge distance 6 is formed between the mutually opposing circular surfaces of the two electrodes 1 and 2, and the discharge distance 6 is determined by the gas pressure and the gas pressure. This determines the operating voltage of the discharge tube.

The degassing, gas filling and sealing of the gas discharge tube takes place in a closed reactor or brazing furnace 8 (FIG. 2) according to a predetermined operating sequence.

This will be discussed later with reference to FIG.

The gas filling chamber 7 of the gas discharge tube contains a preionized medium (pre
Tritium is filled as an ionization medium, and the tritium is diffused and introduced into the gas filling chamber 7 through the insulating wall 3 after the electrodes 1 and 2 and the insulating wall 3 are bonded to each other by brazing. It is now possible to

Preparation of tritium and introduction of the tritium into the gas filling chamber 7 of the gas discharge tube are carried out by the gas introduction device shown in FIG.

The gas introduction device comprises a reactor or brazing furnace 8 in which a large number of gas discharge tubes are accommodated at once, the brazing furnace 8 having a removable flange joint 9 with a metal insert.
and an electrical resistance element 10 that acts as an external heating source.

The space inside the brazing furnace 8 is connected to a vacuum pump 13 via a vacuum valve 11, and is connected via a vacuum valve 12 to a reversible getter pump that functions as a tritium container.
mp) 14.

The galley coupon pump 14 contains powder 15 of a hydride-forming metal, preferably uranium.

The tritium pressure in the gas introduction device shown in FIG. ing.

For brazing, the temperature inside the furnace 8 is measured by a thermocouple 19,
Additionally, a temperature regulator 2 that controls the heating effect of the resistance element 10 is provided.
It is adjusted by adjusting 0.

Next, the operation of the apparatus shown in FIG. 2 will be explained.

The introduction of tritium into the gas discharge tube gas filling chamber 7, which is shown in FIG. 1 and is designed as a closed container or overvoltage protector, takes place according to the following procedure.

That is, (a) First, a large number of gas discharge tubes as shown in FIG. Brazing is performed between the tube electrodes 1 and 2 and the ring-shaped insulating wall 3.

(0) Next, during brazing, the temperature inside the furnace 8 was increased from 800°C to 4°C.
00'C, open the vacuum valve 11, exhaust the gas in the brazing furnace 8 contaminated by the work with the vacuum pump 13, and reduce the pressure in the brazing furnace 8 to 10 to 50 torr. After the contaminated gas is discharged, the valve 11 is closed.

(c) After that, during brazing, the temperature inside the furnace 8 was set to 400 to 50
Keep at 0℃.

(b) Next, a current is applied to the resistive element 18 to raise the temperature of the getter pump 14 and generate tritium.

When the valve 12 is opened in this state, the getter pump 14
The tritium produced is transferred into the brazing furnace 8, and the brazing creates a tritium atmosphere in the furnace.

This tritium atmosphere is maintained for 2 to 10 hours.

For brazing, the tritium transferred into the furnace 8 was described above (1
) and (21), the gas is diffused through the ring-shaped insulating wall 3 of the overvoltage protector and introduced into the gas filling chamber 7.

(e) After the completion of the above diffusion, the temperature of the getter pump 14 is lowered, whereby the tritium that cannot be diffused into the gas filling chamber 7 of the gas discharge tube and remains in the brazing furnace 8 is removed from the getter pump 14. It is returned to the pump 14.

(f) After that, the valve 12 is closed, and the brazing lowers the temperature inside the furnace to room temperature, and the brazing also introduces air or nitrogen gas into the furnace, and the brazing reduces the pressure inside the furnace to atmospheric pressure. Then, for brazing, open the furnace 8 and take out the gas discharge tube.

In the above step), that is, the tritium diffusion step, brazing is performed by maintaining the pressure in the furnace 8 at 30 Torr, the temperature at 450°C, and holding the tritium atmosphere for 5 hours. 'As is clear from equation (2), although it depends on the structure of the ring-shaped insulating wall 3 of the gas discharge tube, there are 10 to iooμCi in the gas filling chamber 7 of the gas discharge tube.
/m' tritium activity can be obtained.

The method according to the embodiment of the present invention applied to introducing tritium into the closed container shown in FIG. 1, that is, the gas discharge tube, has been described above. It can also be applied to introducing a light gas such as hydrogen into a closed container.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a gas discharge tube formed as an overvoltage protector as an example of a closed container to which the method according to the present invention is applied, and FIG. 2 is a gas introduction device for carrying out the method according to the present invention. FIG. 1.2... Electrode, 3... Ring-shaped insulating wall, 4, 5...
・For hard soldering, the joint part, 6... Discharge distance, 7...
Gas filling chamber, 8... Reaction furnace, i.e., furnace for brazing, 9...
Flange joint, 10... Electric resistance element, 11.12.
... Vacuum valve, 13 ... Vacuum pump, 14 ... Reversible getter pump, 15 ... Metal powder for hydride generation, 16 ... Pressure gauge, 17 ... Temperature regulator, 18.
...Electric resistance element, 19...Thermocouple, 20...Temperature regulator.

Claims (1)

[Claims] 1. A method in which a gas, for example tritium, is introduced into a closed container such as a gas discharge tube formed as an overvoltage protector, after the container is sealed, the gas is diffused through the walls of the container to seal the container. A method for introducing a gas into a closed container, characterized by introducing the gas into the container and causing the gas to diffuse at a temperature lower than the temperature at which the closed container is sealed.